Monster
by CoolCordovaProductions
Summary: Life is going great for sans. His family and friends are happy. No more resets are possible. It seems as if everything is going perfectly. Until one fateful day at alphys' lab. An accident causes a chemical DeterminationX contaminate him. What will happen next read to find out.
1. Chapter 1

Sans awakens beside Toriel. He thinks about the events occurring over the past 5 months. After Frisk freed the underground. Everyone had started a new life. Alphys and undyne got legally married. Most of the underground were given jobs, homes, and even the children were allowed into schools.

Unfortunately there was some accidents. On his way home Papyrus was attacked. He wasn't hurt severely, but he was pretty shaken. Besides that everything has been normal. Toriel's teaching at the school. Papyrus is now a chef at a local restaurant. Undyne joined the police force. Alphys joined a group of scientists. Asgore is now part of the local government. Frisk is the ambassador of the monsters. Asriel, Frisk, and Chara are all in school. Muffet has a bake sale. Mettaton and Napstablook both travel around the country performing. Everyone is happy.

Sans's phone starts ringing. He checks it. It's from alphys. She tells him that she's made a discovery in her lab but she needs help. Sans agrees to go. He gets up and gets ready, pulling on a blue sweater and some brown khaki pants. He kisses toriel goodbye, and leaves to alphys'.

Oh! To think he doesn't know what happens next.

Guys I'm Not Dead! I know this chapter is pretty short. Though the next ones are going to be longer. Tune in next time.


	2. The Laboratory

Sans travels to the local Laboratory. Even though he doesn't like using the car and prefers to use his shortcuts instead, he decided that he was too tired to do that right now. He enters in the big white doors. As he walks through the corridors he sees many scientists and janitors none of them alphys. He finally gets to the room that says doctor alphys in large letters on the front of it. He knocks in a small lizard in a lab coat let's him in.

"Hey Alph" Sans greets happily. "Oh h-hi Sans, grab a lab coat I need to show you in my personal lab.", she calmly announced.

He slowly walks through the oak door as alphys opens it. He sees multiple vials of strange green liquid on the desk. The desk was pretty cluttered as well with notes, papers, pens, empty tubes, and empty bowls of ramen.

Alphys speaks, I decided to go do some more research into Determination. I left most of it in my lab in Hot Land. So I went back and collected as much as I could. I noticed on collecting it that it's changed. It's no longer a strange gray color. It's now a sickly green. I've tried everything I don't want to use anymore live test subjects because I'm afraid that something similar to what happened in the true lab will happen again. I know you really skilled in science so I wanted to ask you if you had any idea how I can fix this or what happened." Sans picked up a tube and said," I don't know what happened." The sound of a vial breaking interrupted him. A burner had been turned on by one of the vials and the glass broke the liquid splattered all over Sans. You got his mouth his eyes and all over his clothes. Alphys screams," oh my gosh Sans I'm so sorry that wasn't supposed to happen. Here let me clean you up I'll go grab a rag." Sam's sat there afraid he was going to turn into a melted mess like the amalgamates did. Alphys dubbed the new chemical DeterminationX. After cleaning Sans up and giving him a few checkups to make sure that he was okay. All alphys assured to him that he was going to be fine. He said goodbye the alphys and drove home.

That night he took a shower just to make sure he got all the chemicals off of his body. After exiting the shower he noticed in the mirror that is canine teeth that started to sharpen? He also noticed that his ribs had lifted slightly. Not much is known about skeleton physiology so you just guessed that maybe he was just growing we're going through something all skeletons go through. He goes to bed thinking everything is alright, and snuggles up to Toriel.

That night he has a horrible nightmare. He sees Through The Eyes of an unknown creature attacking members of his family. First frisk, then Cara, then asriel, then toriel, and finally papyrus. He wakes up in a cold sweat thankful it was just a dream. He looks at the clock the neon green letters on the alarm clock say 6 a.m. he decides to get up and get ready for the day.

Though he does not realize yet those dreams may become a reality.

Hey everyone CoolCordova here. So I was really excited to continue this fanfiction. If you have any questions please don't hesitate to ask and I will answer them within the next chapter or will answer them as The Story Goes. I hope you enjoyed this chapter next one should be out possibly tomorrow as it is the weekend for me


	3. The First Attack

The next day Toriel decided it would be a good idea to go to the park. She got everybody dressed and ready to go. As they were driving to the park she noticed that Sans was staring out of the window and not looking at her. She decided it wasn't necessarily a big deal, and so just let it slide.

Sans didn't feel good that day but I knew he would feel bad if he didn't go. He is watching the kids play running around happily. Then asriel tripped and scraped his knee. It wasn't bad and Asriel didn't cry, but seeing the blood caused something strange to happen. Sans growled as a voice in his head said,"Hunt him. He's now helpless." He quickly took away that thought and wondered what happened.

Afterwards toriel drove everyone home. Sans looked in the mirror again and noticed two small bumps on his skull. His molars had sharpened, and he noticed that he had grown 2 inches taller. He went to bed.

That night he had the same dream. Only this time Alphys and Undyne were added to the body count. He woke up in a cold sweat again. He looked at the clock as it said 3 a.m.. He decided to go for a late night walk. As he was walking down the street he noticed somebody else on a late night hike. That same voice in his head said," An easy prey. No one around. It's late at night. Go ahead." He tried to fight it but his blood lust grew stronger. Something over took him. He ran quickly across the street. Body slamming into the young man he knocked him it into a ditch on the side of the road. Using his teeth to tear his flesh. The mans screams echoed through the night. After the feeding he stood up teeth covered in the man's blood. He looked at what he had done terrified. Quickly he went home. He was washing up as toriel walked into the the bathroom.

" Sans what's going on its 4 am", she worriedly spoke. " I'm fine Tori. I just woke up early and decided to go for a run to get rid of some energy. I'm okay don't worry.", he responded. "Oh okay", Toriel said trying to ignore the blood on his shirt and jacket.

Afterwards Sans was so tired he fell asleep as soon as his head hit the pillow.

The body count shall raise.

Hey everybody CoolCordova over here so I'm feeling creative and it's a weekend so I may be posting again tonight so keep tuned in for that. I hope you enjoy this chapter. Please don't hesitate to ask any questions.

Guest: That escalated quickly.

Yes yes it did.


	4. The Transformation

The next day toriel woke up early to make everyone breakfast as it was Sunday morning and she always did this on Sundays. She likes to listen to things when she works so she turns on the radio to listen to The Morning News. She's alarmed to hear that a hiker was mauled to death by an unknown animal the night before. The autopsy showed that he died around 3 a.m. . Around when Sans left she thought. She went back to making the apple fritters that she's famous for. Sans walked into the kitchen.

" Tori, Alphys called and said a party was going tonight with her whole lab and wanted us to go. Even the Napstatons are gonna be there.", he informed. "Oh well I'm down", she answered.

Le time skip

It was 6 p.m. . Toriel and Sans we're getting ready toriel put on a simple but beautiful lavender dress with some purple slip on shoes. Sans wore a simple dress shirt along with some nice jeans. They left to the party and met up with the rest of the Gang. Alphys was in a simple black sequined dress, undyne was wearing a red dress, mettaton was wearing a very nice Bejeweled pink dress along with her iconic boots, as well as all the other gang dressed up very dapper. The music was loud and it was all fine and dandy. Until Sans started feeling dizzy. He started falling and fell into a table of refreshments and then on to the floor. Everyone crowded around him worried. That's when he lost total consciousness.

Sans woke up in an unusual room it looked like a living space. He looked around and saw his friends. "Hey guys what's going on", he questioned. Papyrus answers," Sans you fell onto to a table. We've all been worried about you what's going on you seem so reclusive lately." " I'm fine guys trust me. I'm going to go to the bathroom wash up I'll meet you guys in a minute",he said walking out of the room.

He washed his face in the bathroom. He looked at himself in the mirror, and noticed that his pupils had taken on a yellow color. He looked out the window and saw a bright full moon shining down on him. He felt a surge of energy go through his body. He looked at his fingertips and notice that they've gone from the normal blunt shape into razor sharp claws. He groaned in agony as the rest of his teeth sharpened he grew taller going from his normal 4 foot height to an astounding 7 foot 5. Sharp spines ripped through his shirt. His feet breaking out of his shoes revealing sharp clawed feet. Where the lumps had appeared, Sharp horns appeared. The transformation was almost complete.

Sans felt his mind slipping away from him as he felt animalistic urges the replace his Judgement. He felt as if he was tied up at the back of his mind and an evil presence was at the wheel. The black figure laughed,"I am in control now Sans." The shadow called as he lost full control of his actions.

Just don't hurt my family please.,"Sans begs.

The figure laughs," no promises"

Hey guys CoolCordova here. I'm sorry I know I said I was going to post again on Friday and didn't end up posting on Saturday but I did get sick so please just enjoy this chapter and ask any questions about the story.


	5. Authors note 1

Hey guys so I'm having slight writers block on this story so I'm starting a new undertale story. It's based of titanic and I wanted some ideas for the couples. Chara and Frisk is an idea as well as Sans and Toriel. Please leave some ideas for ships in the reviews. I am also allowing some OCs as extra characters so write some characters as well. Also do not PM me questions ask them in the reviews. I've let it slide but don't y'all start ice skating. Thanks.

Also I will write a long chapter for this story as I finally have a lot of free time.


	6. Chapter 6

All of Sans's friends were sitting in the living room when the sound of splintering wood echoed through the hall. "What was that", Toriel asks. A large skeleton monster appeared in the hall. Frisk shouted for everybody to run, and that's just what they did. They ran through the party room telling everybody to please exit the building and find a safe place. The family and their friends managed to get into the large SUV and the driveway and drive away without Sans. Unfortunately some others were not quite as lucky. The monster attacked a human woman who had almost exited the building. He tore at her as she screamed in agony until she finally died from her injuries. The monster broke through the door frame and managed to catch up with a Bear like Monster in the yard. Loud slashing Was Heard until the bear couldn't fight back anymore. A bunny monster and human man manage to get into their car when they heard a thump on the roof. The sound of glass shattering on the passenger side as the man was yanked out as blood dripped over the side. The bunny monster screamed as the monster broke through her window and yanked her out. There was almost no people outside, so the creature didn't have anything else to prey on. The monster jumped off the car onto the roof of the building and into the forest.

The next morning everybody woke up and was discussing what happened the night before. They were all safe except Chara had tripped on the stairs and broke her ankle. Toriel was freaking out as her husband was missing and multiple of the people were killed in the attack the night before. Frisk was just trying to keep everybody calm. Everybody else was just shaken. Toriel kept calling sans's phone. She started sobbing at the thought that her husband may have been attacked and is possibly dead.

Meanwhile

Sans woke up in the middle of the forest. He groans as he looks around. He notices that he's wearing very tattered clothing and remembers the previous night. He decides that he needs to get home and let his family know he's okay. He Remembers his phone shattering during the transformation. He still most of the forest coming across last night's victims. A dear, a bunny, a turkey, the remains of a male hiker, and some viscera from an unknown animal. He stumbles through the streets and turns to see the Carnage that took place at alphys' residence. It's completely blocked off by police tape but you can clearly see the blood everywhere. He gets home as quick as he can, and knocks on his door. Toriel opens it her eyes widen at the state he's in. "Sans oh my goodness your ok." Toriel sobbed hugging him. Everybody ran to Sans to hug him and ask him what happened. He lied and said that the creature attack him, but he jumped out the back window into the woods for safety. They bought it. "Hey guys I'm BONE-tired right now so I'm gonna go to bed.", Sans calmly says. "SANSSSS", Papyrus groans.

He has the same dream again only Asgore, Muffet, and Mettaton were murdered as well. He hurt himself pleading to the monster in his dream. "Please stop please don't hurt them please", Sans begged. "Oh Sans you don't know the full of it." The figure laughed.

Hey guys CoolCordova here so I'm sorry that I didn't post for a while because school is hard and time-consuming as well as Thanksgiving happened. Thanks for reading and leave your rates and reviews in the Commons. Do not PM me. I'm also working on a Muffet one shot as requested as requested by Barbarian as well as possibly starting work on the Titanic undertale crossover I was thinking about. Also toriel has a close friend that is going to come into place in the next chapter and I want you to submit your original characters in the reviews. The only requirements are they must be female please add their name first and last, age, a short description of what they look like, and some personality I will pick the one that I like the best and that will be the name of the first original character added into the story. Thanks for reading goodbye.


	7. The Love Story

It has been a few days since the accident. Everybody seemed to have moved on. Frisk, Chara, and Asriel are staying at Asgore's home. After some negotiation it was agreed that all 3 children would spend time with Asgore as a father figure. Sans, who had been waking up extremely early, woke up to see Toriel still sleeping. He kissed her on her forehead as he slowly started to cuddle her. He became drowsy again and fell asleep in this position.

Toriel wakes up shortly after. She blushes at the sight of her partner and holds him close. She recalls their story of love. It all started as a small knock on the ruins door as she was sitting. She heard a knock from a particular blue jacket wearing skeleton who practiced knock knock jokes unaware of her presence. He was surprised when she answered. Everyday after that they kept telling jokes. If one wasn't there it was worrying for them. Toriel feared that she was fallen for the mystery man behind the doors. Fearful that a young adult like him could be interested in an old, sad woman like her. After the events of Frisks pacifist run Toriel finally met her mystery man. His name was Sans. Though after seeing him, she wasn't afraid to say he was quite handsome. After a week on the surface with the paperwork of Tempory Free Housing For Monster Citizens was still being worked out all of their family had to live in a small apartment. Sans stayed in Toriel's bedroom. He was pretty silent the first two nights. After that they both started telling their puns, jokes, and pranks to each other much to the annoyance of Papyrus, Sans' 14 year old brother, whom despised anything not taken seriously. One night the two had drunk a small amount, okay large amount, of alcohol. They both just talked nonsense all night long until they both confessed their love for each other. They may have been drunk, but they were sober enough to understand the truth the next morning they were a couple.

After a few weeks of secrecy on Christmas morning they surprised everyone at the celebration by kissing each other passionately under the mistletoe. Everyone was shocked , but most accepted their love. All but three. One of which was Asriel. After finally being freed of his dreaded flower form. It was difficult processing that his happy family had fallen apart in his absense. He cried for hours in his room after hearing the news that his parents had lost their love for each other. As well as Sans being in the picture now was the last straw for the hope of his parents being together.

Chara was a small bit different. She had been a careful observer through all previous fallen humans eyes. She had witnessed the humans die at her adoptive fathers hand. Her hatred of humanity was worsened over time and Every time she was a spectator of this world she was happy to know humanity was getting what it deserves. Frisk came, but she was different. She had freed the monsters instead of fighting. She freed her family. After Frisk saved everyone. Chara became more prominent and begged to be given half of Frisk's soul. She finally was free from the limits of her ghostly form. Afterwards she began seeing signs of a skeleton monster becoming a lover of her mother. Chara one day had enough of him and attacked him. She was given therapy and grew to think," My mom is happy. I will accept him".

Finally Asgore was the hardest to accept the relationship. He still loved toriel and wanted to be with her. He grew jealous and a distaste for Sans. He was silent about it until angrily confronting the skeleton after a witnessed kiss in their home. He was so jealous of his woman being stolen from him that he attempted to assassinate Sans. Though after a while and lots of therapy after that incident. He grew to understand and respect their relationship.

MEANWHILE

Sans had the same dream as many nights before. Though this time it was different. He knew what he looked like in his monstrous state. He could see everything from his appearance to the gore to the sounds of the slaughtering of innocent people. He kept hearing himself begging the blackness in his head to just leave him alone. "Please just leave my family alone don't do a thing to them. Do whatever to me. Leave them out if this.", he screamed. "Oh sans", the figure spoke in a deep voice. "Is this begging going to work? No, its not. I will do what I want to who I want. When I am in control you have no power." It says. It grabs him by his collar and whispers into his ear. "Remember no promises", it rasps.

Hey guys so sorry for the wait got sidetracked with other things. Also happy late Christmas. So I did send another story and it is a soriel story based mostly on Romance. If you're into that go ahead and go 2 my stories and read it. I did work very hard in this chapter though and I would appreciate any comments and reviews so please don't hesitate. Cool Cordova signing off.


	8. The Field Trip

Chapter 7: The trip

This chapter will be focused mostly on Frisk, Chara, and Asriel.

Frisk sat in the car next to their adoptive brother Asriel and sister Chara. They were being driven to school, but today was different. There was a school field trip to a park nearby with a "Special" surprise for them to travel to. The family drove on their daily drive to their school. Frisk rubbed the faded purple seat covers in the car. It felt soft and kind of scratchy. She looked over at Asriel when she noticed was wearing clip on piercings on his ear. "Odd", she thought. She turned to chara wearing a comfortable green t-shirt and black leggings. Frisk looked at her blue shirt and brown leggings. She was nervous as she wasn't the social type and she was afraid that she wouldn't be paired with Chara and Azzy and have to be with someone she didn't know very well or someone who didn't like her. Frisk found a hole in the thigh of her pants, when she made a mental note to fix that the car stopped. They were at the school and said goodbye to her mom and Sans. They walked inside and saw many members of the PTA inside. They offered to chaperone for the "Mystery" field trip.

Chara sat in her classroom as they waited for the buses to pick them up. Chara tapped her desk as she heard someone walk into the room. It was Mr. Manson their friend Tommy's dad. Though they were so different that Chara question their relations to eachother. Tommy was a short,scrawny boy who was quiet, but also was very nice when he opened up to people, as well as being one of the most intelligent people in the class. His dad on the other hand was almost the opposite. He was tall, muscular, and very outspoken. He didn't seem like an idiot, he was just very ignorant. He wasn't very nice especially when it came to the monsters. He hated monsters with a burning passion. He owned a gym and didn't allow monsters to go there. He goes to the PTA meetings and is very rude there. He made comments about Toriel to the other parents. He openly showed his disgust to Alphys and Undynes marriage. He made sexist comments about Mettaton and Muffet. He was just an all around rude person. Chara let us just say, didn't enjoy his presence. "Okay students since is out sick today I will be you're chaperone.", he boomed. You could hear all of the eyerolls in the room. Tommy seemed very nervous in his fathers presence. "Tommy", his father shouted. "Y-yes dad", Tommy's weak voice answered. "Don't answer so scared boy I just want to ask if you want to be paired up with anyone special.", says. "Oh um can I be with Frisk", he asks. His father sighs knowing Frisk freed the monsters, "Ugh fine". Frisk was shocked as Tommy looks at her blushing. They both stared for an awkward amount of time. What Frisk didn't know was that Tommy had a crush on her.

After all of the busses lined up all of the kids went up to the teacher and clasped on bracelets printed with their name to keep track of them. Chara paired up with Asriel who seemed pretty out of it as he clutching his I-Pod Nano with earbuds in. The bus started moving as Tommy sat down next to Frisk. He awkwardly sat as he stared at his lap. Frisk giggles and says," You can talk I don't bite." "Oh sorry, Hi I'm Tommy.", he apologizes. "I'm Frisk I like your shirt.", she says acknowledging the tanktop with a muscular torso printed on it. "Oh this old thing, it was the only tank top I had clean so I had to wear it", he answers. The two keep talking as Asriel and Chara watch. Chara says to Asriel," Oh my god I ship it so hard it's so cute". Asriel looks on suspiciously.

The bus drives for an hour before arriving at the park. There all of the students see Frisks family. Everyone is confused until they see the booths. It is a convention to meet the Town's new residents. Chara and Asriel both go around asking everybody questions while Tommy and frisk do the same. After a while they have a 30 minute free-time/break. Tommy takes Frisk through some bushes until they get to a small oasis. Tommy sits with Frisk as they watch the small fish swim in the beautiful,clear water. Tommy says," Frisk can you close your eyes please I have a gift for you". Frisk complies ad he feels his hands cup her cheeks as he plants his lips on hers. Frisk is surprised at first, but soon kisses back they kiss for 30 seconds until separating. "Well um first kiss at 13", Frisk says. "Yeah that was exiting", Tommy says. What they don't know is that Toriel and Sans were standing behind the brush and watching.

So that's all folks. Hey guys CoolCordova here so how did you like this chapter. If you did don't forget to leave a review. I thought I'd put a bit of fluff in between the horror so how do you like Tomisk, Frommy, Fromisk? Next chapter will be much more serious. Enter your OCs for a chance to be in this story. Check out my YouTube channel for more of my content channel/UCm0VhRG-SKF2uBIee52XyMw Thanks for reading adíos.


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